### Answer Based on the information available, intermittent "permission to perform the transfer" errors are typically related to telephony/SIP trunking issues rather than Retell configuration problems. [(1) ]() Key points to investigate: 1. **Telephony provider issues**: Call transfer functions similarly to placing an outbound call, so failures occur for similar reasons as outbound call failures. The SIP connection log in your call logs can help diagnose the failure reason. 2. **SIP trunk configuration**: If you're using SIP trunking (e.g., Telnyx) , a similar case showed the error was caused by "Unverified origination number" on the provider side. You may need to contact your telephony provider to investigate. [(2) ]() 3. **Displayed Caller ID setting**: One suggestion for this specific error is to set the Displayed Caller ID to the Retell Agent's Number instead of the user's number. [(3) ]() Recommended next steps: - Check the SIP connection logs for the failed calls in your call history [(1) ]() - Review your SIP trunk settings, particularly the outbound transport method (try TCP or UDP) [(2) ]() - Contact your telephony provider if the logs show provider-side errors Since other calls transferred successfully during the same window, this points to intermittent telephony issues rather than a persistent configuration problem.

​ To learn more, see the sources I considered: [[1] Debug call transfer failure](https://docs.retellai.com/reliability/call-performance) [[2] Transfer Call Permission Error - Need Configuration Assistance](https://discord.com/channels/1186424376300679209/1450235811470770359) [[3] Transfer call failure: “probably don’t have the permission to perform the transfer…”](https://discord.com/channels/1186424376300679209/1450603538798608436) ​

Feel free to tag @AI Evy with additional questions. I also appreciate feedback, it helps me improve.